Hibernate 简单地从 JSON 添加元素到 manytomany

Question

我想通过请求在我的 manytomany 关联中添加元素，而不加载每个添加的元素。我正在使用自定义连接 table。 [代码将在底部添加]

例如这是 JSON 我得到：

{
    "id": 122,
    "materials": [
        {
            "id": {
                "materialId": 62,
                "homeworkId": 122
            },
            "position": 1
        }
    ]
}

所以有一份家庭作业材料。如果我将其作为 POST 发送到服务器，则不会发生任何事情（如预期的那样）。对于以下所有示例，我仅使用 homeworkRepository.save(homework)

下面的方法也行得通。（所有作业材料将按预期删除）

{
    "id": 122,
    "materials": []
}

但是如果我想像这样向材质中添加元素：

{
        "id": 122,
        "materials": [
            {
                "id": {
                    "materialId": 62,
                    "homeworkId": 122
                },
                "position": 1
            },
            {
                "id": {
                    "materialId": 162,
                    "homeworkId": 122
                },
                "position": 1
            }
        ]
    }

会报错

attempted to assign id from null one-to-one property [schooling.api.courses.homework.ids.HomeworkMaterial.homework]

所以问题是，材料不是从数据库加载的，我只有 HomeworkMaterial 的 ID。所以我很确定，如果我只是循环遍历 HomeworkMaterials 并从数据库加载所有材料，它就可以工作。但在我看来，这确实不是一个好的解决方案，因为我认为我不需要访问数据库来添加那些 HomeworkMaterials，因为我在客户端上做了这个并且拥有材料的 ID，如果出现问题，只会抛出异常。

所以我的问题是，如何在不获取材料的情况下轻松保存更多的 HomeworkMaterials？

我也试过遍历它们并将它们保存在它们自己的存储库中，但这也不起作用。（得到与以前的方法相同的异常）

所以现在我的代码：

Homework.java

@Getter @Setter @NoArgsConstructor
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
@Entity
@Table(name = "homework")
public class Homework {
private static final String sequenceName = "homework_id_sequence";

@Id
@Column(nullable = false)
@SequenceGenerator(allocationSize=10,  sequenceName=sequenceName, name=sequenceName)
@GeneratedValue(generator=sequenceName, strategy= GenerationType.SEQUENCE)
protected Long id;

@OneToMany(mappedBy = "homework", cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.LAZY)
@Fetch(value = FetchMode.SUBSELECT)
@JsonIgnoreProperties(value = {"homework", "material"})
List<HomeworkMaterial> materials = new ArrayList<>();

public void addMaterial(Material material, int position) {
    HomeworkMaterial homeworkMaterial = new HomeworkMaterial(material, this, position);
    materials.add(homeworkMaterial);
    material.getHomeworks().add(homeworkMaterial);
}

public void removeMaterial(Material material) {
    for (int i = 0; i < materials.size(); i++) {
        HomeworkMaterial current = materials.get(i);
        if(current.getHomework().equals(this) && current.getMaterial().equals(material)) {
            current.getHomework().getMaterials().remove(current);
            current.setHomework(null);
            current.setMaterial(null);
            materials.remove(current);
        }
    }
}
// Equals and Hash omitted
}

Material.java

@Getter @Setter @NoArgsConstructor
@JsonIdentityInfo(scope = schooling.api.courses.materials.Material.class, generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")

@Entity
@Table(name="material")
public class Material implements FileOwner {
private static final String sequenceName = "material_id_sequence";

@Id
@Column(nullable = false)
@SequenceGenerator(allocationSize=10,  sequenceName=sequenceName, name=sequenceName)
@GeneratedValue(generator=sequenceName, strategy=GenerationType.SEQUENCE)
protected Long id;

@OneToMany(mappedBy = "material", cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.LAZY)
@Fetch(value = FetchMode.SUBSELECT)
@JsonIgnoreProperties(value = {"homework", "material"})
List<HomeworkMaterial> homeworks = new ArrayList<>();

public void addHomework(Homework homework, int position) {
    HomeworkMaterial homeworkMaterial = new HomeworkMaterial(this, homework, position);
    homeworks.add(homeworkMaterial);
    homework.getMaterials().add(homeworkMaterial);
}

public void removeHomework(Homework homework) {
    for (int i = 0; i < homeworks.size(); i++) {
        HomeworkMaterial current = homeworks.get(i);
        if(current.getHomework().equals(homework) && current.getMaterial().equals(this)) {
            current.getHomework().getMaterials().remove(current);
            current.setHomework(null);
            current.setMaterial(null);
            homeworks.remove(current);
        }
    }
}
}

作业Material.java

@Getter @Setter @NoArgsConstructor
@Entity
@Table(name = "homework_material")
public class HomeworkMaterial {
@EmbeddedId
private HomeworkMaterialId id;

@ManyToOne(fetch = FetchType.LAZY)
@MapsId("materialId")
private Material material;

@ManyToOne(fetch = FetchType.LAZY)
@MapsId("homeworkId")
private Homework homework;

@Column(nullable = false)
private int position;

public HomeworkMaterial(Material material, Homework homework, int position) {
    this.material = material;
    this.homework = homework;
    this.position = position;
    this.id = new HomeworkMaterialId(material.getId(), homework.getId());
}
}

HomeworkMaterialId.java

@Embeddable
@NoArgsConstructor @AllArgsConstructor @Getter @Setter

public class HomeworkMaterialId implements Serializable {

@Column(name = "material_id")
private long materialId;

@Column(name = "homework_id")
private long homeworkId;

}

如上所述，为了节省我只是简单地使用 homeworkRepository.save(homework)

Answer 1

我找到了一个解决方案，我可以使用 getById“获取”家庭作业和 Material，这样数据库就不会被访问，但我有一个对它们的引用，然后我可以保存它。

Hibernate 简单地从 JSON 添加元素到 manytomany

Hibernate simply adding elements to manytomany from JSON

java

spring

many-to-many

hibernate